Encephalitis

Question 1

Define

Answer 1

There is inflammation of the brain parenchyma, although the meninges are often also affected.

Encephalitis may be caused by:

1. Direct invasion of the brain by a neurotoxic virus e.g. HSV
2. Delayed brain swelling following a dysregulated neuro-immunological response to an antigen, usually a virus (postinfectious encephalopathy), e.g. following chickenpox
3. A slow virus infection such as HIV or subacute sclerosing panencephalitis (SSPE) following measles

Encephalopathy from a non-infectious cause (e.g. such as metabolic disease) may have similar clinical features to infectious encephalitis

In the UK, the MOST COMMON causes of encephalitis are:

• Enteroviruses
• Respiratory viruses e.g. influenza viruses
• Herpes viruses (HSV, VZV, HHV6)

Worldwide, organisms causing encephalitis include:
* Mycoplasma
* B. bordgdorferi (Lyme disease)
* Bartonella henselae (cat scratch disease)
* Rickettsial infections (e.g. Rocky Mountain spotted fever)
* Arboviruses

HSV is a RARE cause of childhood encephalitis but it can be devastating

Question 2

Symptoms and signs

Answer 2

Fever

Altered consciousness, e.g.:
* Psychiatric symptoms
* Emotional lability
* Movement disorder
* Ataxia
* Reduced consciousness

Seizures

Poor feeding, irritability, lethargy

Initially, it may not be possible to clinically differentiate encephalitis from meningitis, and treatment for both should be started

Question 3

Investigations

Answer 3

Same as meningitis

• Bloods- FBC, WCC, LFTs, U&Es, platelets, glucose, coagulation studies
• Lumbar puncture + CSF analysis
• LP contraindications
  1. * Cardiorespiratory instability
  2. Focal neurological signs
  3. Signs of raised ICP (coma, high BP, low HR)
  4. Coagulopathy
  5. Thrombocytopenia
  6. Local infection at LP site
  7. Causes undue delay in starting Abx

PCR for viruses

Serology

EEG, CT/MRI- (focal changes, particularly within the temporal lobes seen with HSV)

hyperintense lesions, oedema, BBB breakdown

NOTE: these tests can be normal initially, so should be repeated if the child is not improving

Question 4

Management

Answer 4

Empirical Therapy
* IV Aciclovir usually given if suspected encephalitis until cause is determined
* Often give empirical antibiotics (e.g. vancomycin + cefotaxime) for potential bacterial origin

Supportive Care
* Endotracheal intubation and mechanical ventilation
* IV Fluids
* Decrease intracranial pressure if elevated
* HSV Encephalitis (proven or suspected)- IV aciclovir for 3 weeks
* CMV Encephalitis- IV ganciclovir and foscarnet for 2-3 weeks
* VZV Encephalitis - aciclovir/ ganciclovir
* IV admin in simple encephalitis

For <2m

10 - 20 mg/kg every 8 hrs for up to 21 days (may be longer if immunocompromised)

For 3m - 11 y/o

500mg/m2 every 8 hours for up to 21 days (in simplex encephalitis)

Body surface area calculation:

Body surface area (m2)= body weight (kg)∗height (cm)‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾√3600

Body surface area = 0.43m2 à 500 * 0.43 = 215mg

IV administration à reconstitute to:

25mg/mL with water

5mg/mL with NaCl

5mg/mL à 215 / 5 = 43mL of NaCl + 215mg aciclovir

For >12 y/o

10mg/kg every 8 hrs for up to 21 days (may be longer if immunocompromise)

Follow up

Supportive, rehabilitation and monitoring should continue for at least 1 year after discharge from hospital

Hearing evaluation should be performed at time or shortly after discharge from hospital

Question 5

Complications

Answer 5

Complications

Focal neurological deficits, neurological sequelae

Mortality

Long-term sequelae- may not arise in acute infection, e.g. motor incoordination, seizures, strabismus, amblyopia, hearing impairment, behavioural disturbances

If untreated, the mortality rate is > 70% and survivors usually have serious neurological sequelae

Prognosis

Varies depending course of infection and patient age

Neurological sequelae may improve in self-limiting cases, focal deficits improve more slowly

At risk of development and/or intellectual disability